Single shaft combined cycle power plant and its operation method

ABSTRACT

According to the invention, there is provided a single shaft combined cycle power plant which can quickly switch from single operation of a gas turbine to combined operation of the gas turbine and a steam turbine, and can quickly increase output power, from low power to high power. The single shaft combined cycle power plant includes a means for maintaining the rotation speed of the steam turbine at a speed slower than but near a rated rotation speed when the steam turbine is separated from a coupled unit of a generator and the gas turbine.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a single shaft combined cycle powerplant which drives a generator by a gas turbine and a steam turbine, andmore particularly to a single shaft combined cycle power plant which isconfigured so that a steam turbine can be separated from and connectedto a coupled unit of a generator and a gas turbine.

2. Description of the Prior Art

A single shaft combined cycle power plant configured so that a steamturbine can be separated from and connected to a coupled unit of agenerator and a gas turbine has been proposed in JP-A-8-177414 (seeFIGS. 4 and 5, and Paragraphs 0016, and 0028 to 0031).

BRIEF SUMMARY OF THE INVENTION

In the above described conventional single shaft combined cycle powerplant, it is possible to perform single operation of the steam turbine,and of the gas turbine. However, when solely operating one of the steamturbine and the gas turbine, the other is stopped from running, so thatit takes a long time to synchronize the steam turbine and the gasturbine for switching from the single operation to combined operation ofthe gas turbine and the steam turbine.

Accordingly, it is an object of the invention to provide a single shaftcombined cycle power plant which can quickly switch from singleoperation of a gas turbine to combined operation of the gas turbine anda steam turbine.

Another object of the invention is to provide a single shaft combinedcycle power plant which can quickly increase output power of agenerator, from low power to high power.

In order to achieve the objects, the present invention provides a singleshaft combined cycle power plant including a means for maintaining therotation speed of a steam turbine at a predetermined speed slower than arated rotation speed (for example, at a speed near the rated rotationspeed) when the steam turbine is separated from a coupled unit of agenerator and a gas turbine.

According to the above described configuration, because the rotationspeed of the steam turbine separated from the coupled unit of thegenerator and the gas turbine is maintained at the speed slower than andnear the rated rotation speed, when connecting the steam turbine to thecoupled unit of the generator and the gas turbine, the rotation speed ofthe steam turbine can be quickly increased to the rated rotation speed,whereby it becomes possible to quickly switch from single operation ofthe gas turbine to combined operation of the gas turbine and the steamturbine. Thus, it is possible to quickly increase output power of thegenerator, from low power to high power.

Other objects, features, and advantages of the invention will becomeapparent from the following description of embodiments of the inventiontaken in conjunction with the accompanying drawings.

Hereinafter, the embodiments of the invention will be described withreference to the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic view of a first embodiment of a single shaftcombined cycle power plant according to the invention;

FIG. 2 illustrates a relationship between the power plant output and therotation speed of a steam turbine of the single shaft combined cyclepower plant as shown in FIG. 1; and

FIG. 3 is a schematic view of a second embodiment of the single shaftcombined cycle power plant according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment of a single shaft combined cycle power plantaccording to the invention will be described below with reference toFIGS. 1 and 2.

The single shaft combined cycle power plant according to the embodimentmainly includes a generator 1, a gas turbine 2 and a steam turbine 3which drive the generator 1, a clutch 4 which is a means for separatingand connecting the steam turbine 3 from and to the generator 1, and acontrol device 5 which detects output change (load change) of thegenerator 1 to output an instruction to separate and connect the steamturbine 3 from and to the generator 1.

The generator 1 shares a rotation axis 6 with the gas turbine 2, or isconnected to a rotation axis 6S of the gas turbine 2.

The gas turbine 2 includes an air compressor 7 which shares the rotationaxis 6S with the gas turbine 2, a combustor 8 which introducescompressed air from the air compressor 7, and a fuel supply system 10having a fuel adjusting valve (or a control valve) which supplies fuelto the combustor 8.

The steam turbine 3 includes a steam supply system 12 having a steamregulating valve 11, a condensed water recovery system 14 which recoversused steam by condensing it using a condenser 13, and a turning device15 connected to the steam turbine 3.

The clutch 4 separates and connects the rotation axis 6 of the generator1 from and to the rotation axis 6B of the steam turbine 3, and is aso-called one-way clutch which separates the rotation axis 6 from therotation axis 6B when the rotation speed of the steam turbine 3 is lessthan that of the generator 1, and connects the separated rotation axis 6to the rotation axis 6B when the rotation speed of the steam turbine 3reaches or becomes faster than that of the generator 1.

The gas turbine 2 includes an exhaust gas system 16 for dischargingexhaust gas which is combustion gas supplied from the combustor 8, andthe exhaust gas is discharged via a heat recovery steam generator 17from a chimney 18.

On the other hand, the condensed water in the condensed water recoverysystem 14 is guided to the heat recovery steam generator 17, heated intohot steam, and then guided to the steam supply system 12.

Further, a steam recovery system 20 including, for example, a controlvalve 19 which opens when starting and stopping the steam turbine, andin an emergency, is guided from the steam supply system 12 before thesteam regulating valve 11 to the condenser 13, so as to bypass the steamturbine 3.

The control device 5 captures a detection signal “a” of a clutchconnection detector 21 which is a means for detecting a separation orconnection state of the clutch 4, a detection signal “b” from a rotationspeed detector 22 which is a means for detecting the rotation speed ofthe rotation axis 6B of the steam turbine 3, and an output signal “c” ofthe generator 1. Then, based on the signals from “a” to “c”, a controlsignal “d” for controlling the fuel adjusting valve 9 and a controlsignal “e” for controlling the steam regulating valve 11 are output.

In the case of the single shaft combined cycle power plant having theabove described clutch 4, at the time of starting, the gas turbine 2 isactivated while the steam turbine 3 is separated from the generator 1,and when the rotation speed is reached to a suitable speed for ignitionof the combustor 8, the fuel adjusting valve 9 is opened according to aninstruction from the control device 5 so as to supply fuel to thecombustor 8. The supplied fuel is mixed with air supplied from the aircompressor 7 to be air-fuel mixture, and the air-fuel mixture is burnedto generate combustion gas. The combustion gas rotates the gas turbine2, and the rotation speed thereof is increased to the rated rotationspeed. The combustion gas used in the gas turbine 2 is introduced intothe heat recovery steam generator 17 as exhaust gas, and then thecondensed water from the condenser 13 is heated to generate steam. Thesteam is supplied from the steam supply system 12 to the steam turbine 3to generate torque in the steam turbine 3. The steam used in the steamturbine 3 is condensed by the condenser 13 and returned to the heatrecovery steam generator 17. After the rotation speed of the steamturbine 3 increases to the rated rotation speed, the steam turbine 3 isconnected via the clutch 4 to the gas turbine 2 of which the rotationspeed has already reached the rated rotation speed.

By the above described series of controls, both the gas turbine 2 andthe steam turbine 3 reach the rated rotation speed, so that rated poweris output from the generator 1.

In the case that the need for reducing the output of the generator 1arises if load change occurs during the above described operation, forexample, if a load connected to the generator 1 decreases, it is thoughtthat the output of both the gas turbine 2 and the steam turbine 3 shouldbe reduced. However, in accordance with a recent emission regulation ofenvironmental pollutants, for example, nitrogen oxides (hereinafterreferred to as NOx), the gas turbine adopts a low-NOx combustor andthus, the output of the gas turbine cannot be easily reduced togetherwith the steam turbine. That is, in order to minimize the amount of NOxemission, misfire, and backfire of the low-NOx combustor, the output ofthe gas turbine must be maintained, for example, at 75% output at thelowest.

For this purpose, in the present embodiment, as shown in FIG. 2, theoutput of the generator 1 becomes lowest when the gas turbine 2 issingly operated. Further, when the steam turbine 3 is separated from thegenerator 1, in other words, when the control device 5 receives thedetection signal “a”, which indicates the separation of the steamturbine 3, from the clutch connection detector 21 which is the detectionmeans, the detection signal “b” from the rotation speed detector 22which is the detection means is captured to generate the control signal“e” to control the opening degree of the steam regulating valve 11 so asto maintain the rotation speed of the steam turbine 3 at a speed slowerthan the rated rotation speed (for example, 3000 rpm) and near the ratedrotation speed (for example, 97% of 3000 rpm).

When the rotation speed of the steam turbine 3 is maintained at 97% ofthe rated rotation speed, the clutch 4 remains separated, and thus thesteam turbine 3 remains separated from the generator 1 connected to thegas turbine 2.

When the control device 5 controls the opening degree of the steamregulating valve 11 so as to maintain the rotation speed of the steamturbine 3 at 97% of the rated rotation speed, excessive steam resultingfrom limitation by the steam regulating valve 11 is recovered into thecondenser 13 via the control valve 19 and the steam recovery system 20.

Thus, in this embodiment, the clutch connection detector 21, therotation speed detector 22, the control device 5, and the steamregulating valve 11 operate as a means for maintaining the rotationspeed of the steam turbine 3 at the speed slower than but near the ratedrotation speed.

In this way, the generator 1 can be driven solely by the gas turbine 2.In this situation, if the control device 5 detects increase in load bythe output signal “c” of the generator 1, the control device 5 sends thecontrol signal “e” to open the steam regulating valve 11 to increase theamount of steam supplied to the steam turbine 3, so as to increase therotation speed of the steam turbine 3 up to the rated rotation speed.When the rotation speed of the steam turbine 3 is increased to the ratedrotation speed, the clutch 4 is then connected to cause combinedoperation by the gas turbine 2 and the steam turbine 3. In thisswitching from the single operation of the gas turbine 2 to the combinedoperation of the gas turbine 2 and the steam turbine 3, the rotationspeed of the steam turbine 3 can be increased to the rated rotationspeed in a short time because the steam turbine 3 is in a standby statewith the rotation speed being maintained at 97% of the rated rotationspeed, whereby the combined operation can be recovered in a short time.

The above described switching between the combined operation and thesingle operation (namely, a load change occurs in a short time, and thenecessity of addressing a load change in a short time) occurs during theday in the case of a power plant for selling electricity or a housepower plant for complying with electric power demand in a factory, forexample, while no frequent load change occurs during the night.

Accordingly, when the operation shifts from the daytime operation withload change in a short time to the nighttime operation with no loadchange and with the load being reduced, the rotation of the steamturbine 3 is stopped in a state of the steam turbine 3 being separatedfrom the generator 1 and the gas turbine 2, or the gas turbine 2 issolely operated while the steam turbine 3 is rotated at a low speed of10 rpm, for example, by the turning device 15.

Then, when a time zone in which the load changes in a short time comeson the following day, steam is supplied to the steam turbine 3 tomaintain the rotation speed of the steam turbine 3 at the speed slowerthan the rated rotation speed but near the rated rotation speed (97% ofthe rated rotation speed) and bring the steam turbine 3 in a standbystate, while continuing the single operation of the gas turbine 2.

During the standby state, when the time zone in which the load changesin a short time comes and the load is increased, the amount of steamsupplied to the steam turbine 3 is increased to increase the rotationspeed of the steam turbine 3 up to the rated rotation speed, and thenthe steam turbine 3 is connected to the generator 1 connected to the gasturbine 2 to perform the combined operation, as described above.

In the above described embodiment, although the steam turbine 3 isseparated from and connected to the generator 1 connected to the gasturbine 2, the invention is not limited to this. Specifically, as shownin a second embodiment in FIG. 3, the steam turbine 3 may be separatedfrom and connected to the gas turbine 2 connected to the generator 1,whereby the same operational advantage as the first embodiment can beobtained.

In the above embodiments, although the clutch connection detector 21,the rotation speed detector 22, the control device 5, and the steamregulating valve 11 are described as a means for maintaining therotation speed of the steam turbine 3 at the speed slower than but nearthe rated rotation speed, it may be possible to provide the turningdevice 15 or other rotation devices as a means for maintaining therotation speed at a speed slower than but near the rated rotation speed.In this case, the control device 5 having received the detection signals“a” and “b” from the clutch connection detector 21 and the rotationspeed detector 22 should indicate an appropriate rotation speed for theturning device 15 and other rotation devices during the standby state.

As described above, according to the invention, there is provided asingle shaft combined cycle power plant which can quickly switch fromsingle operation of a gas turbine to combined operation of the gasturbine and a steam turbine, and can quickly increase output power, fromlow power to high power.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on the embodiments ofthe invention, the invention is not limited thereto and various changesand modifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A single shaft combined cycle power plant comprising: a gas turbine;a steam turbine; a generator driven by the gas turbine and the steamturbine; a means for connecting or separating the steam turbine to orfrom a coupled unit of the generator and the gas turbine; and a meansfor maintaining the rotation speed of the steam turbine at apredetermined speed slower than a rated rotation speed during the steamturbine is separated from the coupled unit of the generator and the gasturbine.
 2. A single shaft combined cycle power plant comprising: a gasturbine; a steam turbine; a generator driven by the gas turbine and thesteam turbine; a means for connecting or separating the steam turbine toor from a coupled unit of the generator and the gas turbine; a means fordetecting the separation of the steam turbine; a means for detecting therotation speed of the steam turbine; and a control device for directinga limit of the amount of steam supplied to the steam turbine after theseparation thereof, on the basis of detection signals from the means fordetecting the separation and the means for detecting the rotation speed.3. The single shaft combined cycle power plant according to claim 2,further comprising a steam recovery system for recovering excess steamcaused by said limitation of the amount of supplied steam. 4-8.(canceled)
 9. A single shaft combined cycle power plant comprising: agas turbine; a steam turbine; a generator driven by the gas turbine andthe steam turbine; a clutch for connecting or separating the steamturbine to or from a coupled unit of the generator and the gas turbine;and a means for controlling the amount of steam supplied to the steamturbine so as to be a limited steam supply amount so that the rotationspeed of the steam turbine is reduced in comparison with a ratedrotation speed, during the steam turbine is separated from the coupledunit of the generator and the gas turbine.